Costa Rica's Legislative Assembly on Monday passed a measure – by accident – that could legalize same-sex civil unions as part of a larger bill, lawmakers noted on Tuesday.

Conservative lawmakers voted for the bill’s passage without recognizing the included language that could be interpreted to change the definition of marriage, according to the daily La Nación. Lawmakers immediately called for President Laura Chinchilla to veto the bill.

José María Villalta, a lawmaker from San José, inserted the language into the bill. Villalta is a member of the leftist Broad Front Party. The language confers social rights and benefits of a civil union, free from discrimination, according to La Nación.

Villalta attached the measure to a reform of the Law of Young People, which covers various social services for young people and laws governing marriage.

“During the discussion in the first debate, we explained that the Law of Young People should be interpreted with this sense of opening to gays and no one objected,” Villalta said, according to La Republica.